1. Field of the Invention
The present invention relates to microorganisms that have the ability to make fusaric acid (a substance that causes vine-splitting to members of the gourd family, tomato blight or the like) non-toxic to plants, and a method for detoxifying fusaric acid by the use of the microorganisms.
2. Description of the Prior Art
It is known that the genus Fusarium contains species that can cause diseases of wither and blight that can occur during the growth of plants. Diseases such as vine-splitting in members of the gourd family such as cucumbers, watermelons, melons, etc., tomato blight, half-wither disease of eggplants, yellow blight of strawberries, dry rot of devil's foot root, spring blight of grass, etc. are infection of species of Fusarium, named Fusarium oxygsporum fusarium monitiform, Fusarium moniliform, as well as a large number of other species. These fungi contaminate the soil, and are absorbed into the plant from the soil via the xylem. It is thought that the cause of the withering of plants is the fusaric acid that is produced by the metabolism of these fungi. Fusaric acid is produced by almost all species the belong to the genus Fusarium (including the two species mentioned above) that are plant pathogens. This fusaric acid acts as a non-specific toxin, and it damages not only the host plants but also other kinds of plants. Fusaric acid causes an increase in the permeability of plant protoplasmic membranes with respect to tissue fluids that contain Ca.sup.+, K.sup.+, Na.sup.+, or other cations, or that contain various kinds of amino acids, which increase causes exudation of the tissue fluids to surfaces such as those of the leaves of the plant. This exudate dries, and the surfaces of the plants develop high osmotic pressure, which increases the evaporation of water still more. As a result, the plant wilts an dies.
Chemical agents that are used to prevent Fusarium infections include, for example, the o-phenylenediamine derivative include, for example, the o-phenylenediamine derivative with the structure shown below, with the trade name Topjin-M which is used as a soil fungicide. ##STR1## This agent kills the fungi of the genus Fusarium that line in the soil, but if it is merely scattered on the surface of the soil, it is not effective, so it is necessary to mix it into the soil before sowing or planting. This operation requires much labor. There is also the disadvantage that once the symptoms of the infection have appeared, this agent has almost no effect on stopping the progress of the disorder.
There is a variety of tomato that is resistant to infections caused by Fusarium. It has been found that, in the tissues of this variety of tomato, as shown below, fusaric acid (I) is metabolized and decomposed to form N-methylfusaric acid amide (II). The decomposition of fusaric acid is effectively attained among varieties of tomatoes that have strong resistance to Fusarium infections. ##STR2##
As described above, fusaric acid causes vine-splitting to members of the gourd family, as well as tomato blight or the like. In view of tomatoes having resistance to the above-mentioned infectious diseases, the diseases of plants caused by fusaric acid can be prevented by decomposing or chemically modifying fusaric acid so as to make the fusaric acid non-toxic to plants.